1. Field of the Invention
This invention concerns a zinc alloy containing gallium and indium for use with electrode.
2. Description of the Prior Art
Zinc has hitherto been utilized popularly as electrode material, for example, in electric cells, electric plating and cathodic protection, since zinc, although being a base metal, provides a relatively high hydrogen overvoltage and excellent corrosion resistance, as well as it is available at low cost.
Electrode (cathode) material for use in a dry cell, for instance, has to satisfy the required conditions of causing neither deformation in the cell vessel nor leakage of liquid due to local corrosion or attendant evolution of hydrogen gas. However, usual zinc when used alone in the form of metal can not always satisfy the conditions in such uses partly due to the presence of impurities.
A typical measure generally taken so far for improving the nature of zinc for use with electrode has been the amalgamation of zinc, that is, amalgamation of the inner wall of a zinc can (in contact with electrolyte) in a manganese dry cell or amalgamation of zinc powder (mixed with electrolyte) in an alkali-manganese dry cell. Such amalgamation can effectively increase the hydrogen overvoltage of the zinc electrode, improve the corrosion resistance during storage and suppress the evolution of hydrogen gas. Although the use of mercury for the amalgamation much contributes to the improvement of the dry cell, substitution of mercury with other materials and alternative procedures for the amalgamation have, indeed, been demanded in recent years in view of the prevention of public pollution. As a countermeasure, while the addition of lead, cadmium, indium and the like to zinc has been attempted, none of them can completely overcome the trouble of local corrosion or gas evolution and, accordingly, the use of mercury is still inevitable at present.
Japanese Patent Publication No. 3204/1958 (Sho 33-3204) discloses that the corrosion resistance of zinc in the electrolyte of a dry cell can be improved by the addition of 0.0001-2.0% of indium to zinc. However, the present inventors have made a study on the hydrogen overvoltage having a direct concern with the evolution of hydrogen gas upon discharge of the cell and, as the result, found that although the addition of indium to electrolytic zinc at 99.99% purity is somewhat effective only within a range between 0.01-0.03%, the merit within the range is not so remarkable and the addition of indium out of this range even gives rise to an adverse effect (the reason therefor is not clear at present but it may be considered that the merit obtained by the sole addition of indium is unstable being sensitive to the effect of other impurities).